<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script src="js/jquery-3.3.1.min.js" type="text/javascript" charset="utf-8"></script>
	<script type="text/javascript">
		$(function(){
			$("button").click(function(){
				console.log("button")
				//alert();
			})
			$("select").change(function(){
				console.log($(this).val())
			})
			$("#txt").focus(function(){
				if($(this).val()==="")
				   $(this).val("账号")
			})
			$("#txt").focus(function(){
				if($(this).val()==="账号")
				   $(this).val("")
			})
			$("button").mousemove(function () {
					$(this).css("color","red")
				})
				$("button").mousemove(function () {
					$(this).css("color","black")
				})
				
				$("button").hover(function () {
					$(this).css("color","red")
				},function () {
					$(this).css("color","black")
				})
				
				//对多个函数的处理函数一样，可合并
				$("#txt").on("click dblclick",function () {
					console.log(1)
				})
		})
	</script>
	</head>
	<body>
		<div class="div">
			<button type="button">点击</button>
		</div>
		<select name="">
			<option value="1">足球</option>
			<option value="2">篮球</option>
			<option value="3">乒乓球</option>
		</select>
		<input type="text" id="" placeholder="你好" />
		<input type="text" id="txt" value=""  placeholder="账号" />
	</body>
</html>
